Topic 5.1 Cellular respiration Flashcards
Define cellular respiration
the process by which food is broken down to yield ATP, which is used as a source of energy for metabolic reactions
What’s the respiratory substrate?
the substance oxidised during cellular respiration
Define aerobic respiration
the from of cellular respiration that takes place in the mitochondria in the presence of oxygen
What are stalked particles?
structures where ATP production takes place on the inner mitochondrial membranes
Define reduction
the addition of electrons to a substance e.g. by the addition of hydrogen or the removal of oxygen
Define oxidation
the removal of electrons from a substance e.g. by the addition of oxygen or removal of hydrogen
What is a hydrogen acceptor?
a molecule which receives hydrogen and becomes reduced in cell biochemistry
What’s NAD?
a coenzyme that acts as a hydrogen acceptor
What’s reduced NAD?
NAD which has accepted a hydrogen atom in a metabolic pathway
What is glycolysis?
the first stage in cellular respiration, which takes place in the cytoplasm and is common to both aerobic and anaerobic respiration
What is pyruvate?
the end-product of glycolysis
What’s the purpose of aerobic respiration?
- produces ATP, which can be hydrolysed to ADP and Pi
- releases energy for metabolic reactions/ phsophoylate compounds to make them more reactive
Name the 4 main stages of aerobic respiration and where they occur
Glycolysis- cytoplasm
Link reaction- matrix of mitochondria
Krebs cycle- matrix of mitochondria
Electron transport chain- membrane of cristae
Outline the stages of glycolysis
- glucose is phosphorylated using ATP by adding 2 phosphate groups (phosphorylated sugar is more reactive and unable to pass through the cell membrane)
- phosphorylated sugar is split into 2 x 3C sugar glycerate-3-phosphate (GP)
- 2 x GP converted into 2 x pyruvate (3C), NAD to NADH by hydrogen atoms from GP- 4x ATP molecules produced. phosphorylation of sugar reversed and pi used to convert ADP-> ATP
net gain of 2x reduced NAD and 2x ATP per glucose
How does pyruvate from glycolysis enter the mitochondria?
via active transport
What happens during the link reaction?
- pyruvate crosses the mitochondrial membrane and enters the mitochondria
- pyruvate is decarboxylated by decarboxylases and a molecule of CO2 is produced
- the 2C compound joins with coenzyme A to form acetyl coenzyme A
- at the same time pyruvate is oxidised, losing hydrogens to NAD which results in NADH (NADH used later in ETC)
- energy contained in the acetyl coenzyme A is released into the Krebs cycle
Give a summary equation for a link reaction
pyruvate + NAD + CoA —> acetyl CoA + reduced NAD + CO2
What happens in the Krebs cycle?
- oxaloacetic acid (4C) combines with acetyl coenzyme A (2C) to form citrate (6C)
- citrate is decarboxylated so CO2 is given off and oxidised which means NAD is reduced to NADH to form a 5C compound
- the 5C compound gets decarboxylated, oxidised (which reduces 2 x NAD to NADH and 1 x FAD to FADH2) and phosphorylated which produces ATP from ATP. this forms oxaloacetic (4C) acid again
What is the electron transport chain?
a series of carrier proteins embedded in the membrane of the cristae in the mitochondria
What is the process the ETC uses to produce ATP in aerobic respiration?
oxidative phosphorylation via chemiosmosis
What happens in the electron transport chain?
- electrons released from NAD and FAD undergo redox reactions (NADH and FADH2 are oxidised)
- energy released is coupled in maintaining proton gradient (H+) or released as heat
- oxygen acts as final electron acceptor
How is the H+ gradient established during chemiosmosis in aerobic respiration?
some energy released in the ETC is used to actively transport H+ ions from the mitochondrial matrix to the intermembrane space
How does chemiosmosis produce ATP?
H+ ions move down the concentration gradient via ATP synthase (channel protein) from the intermembrane space to the matrix
ATP synthase catalyses ADP + PI —> ATP
What’s the role of oxygen in the ETC?
final electron acceptor (produces water)
State the benefit of an ETC instead of a singe reaction
- energy is released gradually
- less energy released as heat
What is anaerobic respiration?
form of cellular respiration, takes place only in the cytoplasm when there is no oxygen present
State the stages of anaerobic respiration
1) Glycolysis: glucose is phosphorylated using ATP to add 2 phosphate groups. it is then split to form 2 x glycerate 3-phosphate (GP), a 3 C sugar. GP is then converted in multiple steps into pyruvic acid.
net gain of 2 ATP molecules
2) pyruvate from glycolysis is converted into lactic acid
Explain the role of the Krebs cycle
- completely oxidises pyruvate/acetyl Co A
- to release as much energy as possible
- to generate ATP
- to produce reduced coenzyme/NADH
- so that ATP can be produced in the ETC/by oxidative phosphorylation
How many molecules of NADH, FADH2 and ATP are produced from one molecule of pyruvate going through the krebs cycle?
3 x NADH
1 x FADH2
1 x ATP
